In French Polynesia, the cyclopoid copepod Mesocyclops aspericornis was inoculated into burrows of the land crab Cardisoma carnifex and into tree holes, drums, wells, and tires. It successfully reduced larval populations of Aedes polynesiensis and/or Aedes aegypti by 91-99%. Mesocyclops aspericornis has persisted to date for 29 mo in crab holes and for 60 mo in some wells, tires, and tree holes. As M. aspericornis does not effectively reduce Culex populations, copepod suspensions can be mixed with Bacillus thuringiensis var. israelensis, without detriment to the copepod, to effectively kill larvae of both genera. Its oligophagic feeding pattern, ease of mass production or collection, and high fecundity within probable temperature and salinity ranges of 23-30°C and O-4% make M. aspericornis a good candidate as a biological control agent.

The distribution of organophosphate and carbamate resistance was investigated in 33 samples of Culex pipiens quinquefasciatus Say from 25 cities in Côte d'Ivoire and Burkina Faso. Organophosphate resistance levels were higher in Côte d'Ivoire than in Burkina Faso. Chlorpyrifos resistance ratios at LC95 ranged from 4 to 30 times in Côte d'Ivoire and from 3 to 6 times in Burkina Faso. For temephos, ratios ranged from 3 to 18 and from 1 to 2, respectively. Of 27 samples from Côte d'Ivoire, 25 also displayed cross resistance to carbamates as shown by a mortality plateau in bioassays with propoxur and carbosulfan (similar to chlorpyrifos). Cross resistance to organophosphates and carbamates was caused by an insensitive acetylcholinesterase allele (AceR). This gene was absent from Burkina Faso, except in Niangoloko near the Côte d'Ivoire border. Organophosphate resistance also was associated with the presence of A2-B2 overproduced esterases which had higher frequencies in Côte d'Ivoire (75-100%) than in Burkina Faso (40-50%). Two other esterases with the same electrophoretic mobility as C2 from Puerto Rico and B1 from California were identified for the 1st time in West Africa. "C2" was widespread, whereas "B1" was present in only a few mosquitoes from Côte d'Ivoire. These differences in resistance patterns should be taken into consideration in planning urban mosquito control strategies within 2 countries.

In most of the 130 islands of French Polynesia, the stenotopic mosquitoes Aedes aegypti (the main local vector for the viruses causing dengue) and Aedes polynesiensis (the main local vector of Wuchereria bancrofti) share many breeding sites in water containers such as discarded cans, coconut shells, buckets and water-storage pots and drums. In addition to selective application of insecticides, non-polluting methods of controlling these mosquitoes have been evaluated during the last decade in two main ecological situations: (1) villages, where Aedes breeding sites are typically peridomestic; and (2) flooded burrows of land crabs, the major source of Ae. polynesiensis throughout the South Pacific region. Large-scale trials of biological control agents, such as mosquito fish (Gambusia affinis and Poecilia reticulata) and copepods (Mesocyclops aspericornis), and of integrated-control strategies have demonstrated the efficacy of certain techniques and control agents against the target Aedes populations in some village situations. Generally, mechanical methods (the use of layers of polystyrene beads against mosquito larvae and pupae, and screening against adult mosquitoes) were more efficient than use of the biological control agents. By integrating several methods of control, mosquito densities (as measured by human-bait collections and larval surveys) were reduced significantly compared with the results of concurrent sampling from untreated villages, and control remained effective for months after the interventions ceased. In land-crab burrows, the first attempts to control Aedes larvae used bacterial agents (Bacillus thuringiensis) and predatory copepods gave disappointing results. Mesocyclops aspericornis could be an effective control agent if the burrows were constantly flooded, but most burrows dry out and refill periodically, so copepod populations do not survive. As it proved difficult to reach all corners of the long sinuous burrows with any control agent, larvicidal (chlorpyrifos-methyl) baits were developed for foraging crabs to carry into their burrows. This novel technique proved to be effective and could become the method of choice for treating crab burrows. Further research is underway to find the optimum (biological or chemical) larvicidal ingredient for the crab bait. Despite the ecological and logistical challenges of controlling the Aedes vectors of the dengue viruses and W. bancrofti in so many scattered islands, the French Polynesian experience indicates that relatively simple methods can be integrated and applied effectively and economically. Operationally, however, success also depends on a strong political commitment and on at-risk communities that are sufficiently motivated to maintain a good level of Aedes control.

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